Adolescent obesity is a major public health issue for America: 34% of US adolescents ages 12-19 years are overweight or obese. The impacts of obesity on teenagers are found in many psychosocial and medical comorbidities; overweight and obese adolescents are also at high risk of becoming obese adults with lifelong associated risks. We propose a unique project to examine fundamental aspects of circadian and sleep biology, chemosensory perception, and psychophysiology that can influence food choices and food consumption and may differ between obese/overweight (OW) and normal weight (NW) adolescents. Healthy OW and NW boys and girls ages 12 to 15.9 years will live at home on a strict sleep/wake schedule for 2 weeks and then enter the lab for 11 consecutive days. Sleep/wake during the in-lab session are scheduled on a 28-h day, followed by a 32-h extended waking episode and a 4-h sleep. In-lab assessments include measures of sleep (polysomnography), chemosensitivity (taste and smell), arousal (multiple sleep latency test), circadian time (salivary melatonin), vigilance, impulse control, attentional bias, distraction, satiety, and hunger. Fasting levels of leptin, ghrelin, glucose, insulin, and cortisol will be measured at 6 circadian phases and compared across weight groups. Food choices and food consumption will be monitored throughout as the principal dependent variables. Specific hypotheses are: (1) OW will have later baseline circadian phase (dim light melatonin onset-DLMO) and longer intrinsic circadian period than NW; (2) OW will have reduced slow wave sleep at baseline and in response to extended wakefulness; (3) OW will select higher calorie food and consume more calories at later circadian phases than NW; (4) OW will select higher calorie food and consume more calories than NW later in the waking day. The influence of other measures (e.g., chemosensitivity, arousal, impulse control, etc.) in weight-group differences will be explored with latent growth modeling. Descriptive analyses and exploration of sex differences will also be performed. Findings from this study may bring to light specific eating-related risks factors for OW teens, may provide targets and strategies for countermeasures to prevent or ameliorate overweight and obesity in adolescents and the distress that ensues and may suggest ways to enhance weight loss interventions.